In certain data message communication systems, a central station data base collects inquiry messages or "transactions" from and distributes response messages to data terminals. In systems of this type, it is often desirable to provide polling apparatus (sometimes called a controller) which sequentially polls the several terminals to determine whether they have available messages. More specifically, the polling apparatus connects to each terminal and thereafter interchanges control signals with the terminal in accordance with a communication procedure or protocol, which protocol involves a procedure of signal interchange that advises the terminal that it is being polled, advises the controller whether a message is available, enables the controller to recognize the correct reception of a complete message and advises the terminal that the controller correctly received the message.
A polling system arranged to provide the above-described polling is described in U.S. Pat. No. 4,100,533 issued to O. Napolitano et al on July 11, 1978. The Napolitano et al arrangement utilizes a multipoint switch which, in response to selection signals, connects each of a plurality of terminals to a central controller. These selection signals are generated by the controller polling apparatus which has stored therein a list of items, each item defining the appropriate selection signals for a corresponding one of the terminals. The controller sequentially accesses each item in the list to enable the generation of the appropriate selection signals whereby the multipoint switch connects the controller to the corresponding terminal. The controller then proceeds to interchange the control signals to query the terminal and collect the message or proceed to the next terminal by accessing the next item on the list.
Data terminals are produced by many different manufacturers, each manufacturing service providing various advantageous features. In large data message communication systems, it is often desirable to utilize terminals of different manufacturing sources at different ones of the remote locations. It may also be desirable to utilize a terminal of one source at one remote location during one period of time and a terminal of a different source during another period of time. Unfortunately, the several manufacturers of terminals do not produce machines using the same communicatiion procedures. For example, one terminal may be queried through the use of a prolonged carrier signal while another through the use of a data character sequence which includes a character or characters individual in the communication system, to this machine. In addition, one machine may terminate messages with a character sequence differing from other machines or look for acknowledgements for its message differing from other machines. Accordingly, to provide a polling system for terminals from different manufacturers, it is necessary for the central controllers for each terminal polled to send the appropriate selection signals while using the appropriate communication procedure (protocol) to connect the poller to the terminal, then interchange the appropriate control signals to query the terminal and finally intercommunicate during and after the message with the appropriate protocol.
It is an object of this invention to provide a polling system accommodating data terminals arranged to utilize different communication procedures. It is a further object to provide different procedures without substantial changes in the system each time a terminal is changed.